Electronic motor control for printing presses and the like



2 Sheets-Sheet l W. H. ELLIOT PRESSES AND THE LIKE ELECTRONIC MOTOR CONTROL FOR PRINTING Aug. 31,1948.

Filed April 9, 1945 Aug. 31, 1948.

W. H. ELLiOT ELECTRONIC MOTOR CONTROL FOR PRINTING PRESSES AND THE LIKE Filed April 9, 1945 2 Sheets-Sheet 2 LINE VOLTAGE L m I Q Q g E '3 3 g E 1 MIN.

0 UMSTABLE USEFUL RANGE I00 ruaz CONDUCT/0N @fkcENTAGE 0F FULL CONDUCT/0N) L L L MINIMUM VALUE FOR JTABLE CONDUCT/0N u/vs TABLE USEFUL RANGE TUBE CONDUCT/0N @EECENTAGE 0F FULL CONDUCT/0N) 45324 8 til Patented Aug. 31, 1948 ELECTRONIC MOTOR CONTROL FOR PRINT- ING PBESSES AND THE LIKE William H. Elliot, Shorewood, Wls., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application April 9, 1945, Serial No. 587,245

15 Claims.

1 The invention relates to the control of alternating current motors and, while not limited thereto, it is especially suitable for the automatic speed control of polyphase induction motors, and,

more particularly, motors of the slip-ring type.

The speed of slip-ring type motors, which are required to exert a relatively constant torque, may be varied between zero and synchronous speed by varying the resistance in the secondary circuit. As the commutation of the secondary resistance involves mechanical elements having inertia and electrical circuits having inductance, such speed control is not suitable when the torque required of the motor varies rapidly, as for any given adjustment of the secondary resistance the speed varies substantially inversely as the torque. Furthermore, if the torque required under certain operating conditions is only a small fraction of the normal torque of the motor, while at the same time the speed required is only a small fraction of the normal speed, and at other times the speed and the corresponding torque are high, the material required for the secondary resistance and the amount of apparatus for commutating such resistance become abnormally high and complicated. It has therefore become customary under these conditions to employ special means such as multi-speed motors with'a pluralit of primary and/or secondary windings or two separate motors, one for the high speeds and torques and the other for the low speeds and low or high torques. Where two motors are employed, the motor for the low speed may be geared down so as to afford high torque with a small motor.

The present invention obviates the aforementioned disadvantages. It employs a system which, operating with a, single standard induction motor, affords accurate maintenance of any desired speed between zero and maximum speed for any load between zero and the maximum torque which the motor is capable of exerting and irrespective of the rapidity oi variations of the load imposed upon the motor.

A preferred form of the system embodying the present invention employs a three-phase sliprlng type induction motor which is provided with s. commutatable secondary resistor and with a variable impedance in one of the three lines to the primary terminals of the motor. By increasing this impedance, the primary magnetic field of the motor becomes unbalanced and this results in a reduction in the torque exerted by the motor, such reduction varying with the amount of unbalance.

Figure 1 of the accompanying dra wl ngs illustrates the relation of the phase currents supplied to an induction motor and the torque exerted by the latter. The diagram illustrates stalled characteristics for an induction motor having a given secondary resistance and it will be noted that when the currents of the three phases are balanced the torque is a maximum, whereas the torque decreases with the unbalancing of the phase currents and becomes zero when the current in one of the phases is zero.

As shown by the diagram, the current I in phase 3 is gradually reduced from its maximum value to zero. When the current in phase 3 is a maximum, the currents I and I in phases l and 2, respectively, are also a maximum and equal to the current in phase 3. As the current in phase 3 is reduced, the currents in phases l and 2 remain substantially constant, although they slightly difler from each other due to the dissymmetry created by the unbalancing. When the current in phase 3 is zero, the currents in phases I and 2 are again equal to each other and substantially equal to the current obtaining when the phases are balanced. Similar conditions to those described obtain with any adjustment of the secondary resistance except that the primary current values are proportionally increased or decreased, and the same relation holds true for various speeds especially for very low speeds of the motor. At higher speeds, the conditions are somewhat modified due to the counter-magnetomotive forces of the rotating secondary winding. However, the present control of the impedance in one line to a polyphase motor is primarily of interest in connection with a high secondary resistance for the attainment and regulation of a low speed with varying torque. The variable impedance may be an electron tube or tubes, the impedance of which is controlled by means of a voltage impressed upon the control electrode of the tube. The invention will be more fully explained in connection with the accompanying drawings which illustrate an embodiment of the invention for the control of a threephase induction motor driving a printing press or the like, and which is required to operate at adjustable relatively high speeds at normal torques, must start with a relatively high torque and for threading the paper into the machine must be operable at a very low speed requiring a relatively high torque.

The present invention has for one of its objects to provide special means which aflord a wide range in speed and simultaneously 3 I a wide range in torque with a single motor.

Another object of. the invention is to provide speed regulating means which are rapid in response to varying conditions in load.

Another object is to provide means aflording in an induction motor drive low stablespeeds for rapidly varying loads on the motor.

Another object is to provide a single motor drive affording high torques up to the maximum motor torque at very low constant speed.

Another object is to provide means for quick 5 stoppage of an alternating current motor by dynamic braking.

Another object is to provide in a system of the aforementioned type a regulating impedance which is continuously variable between substantially zero and infinity.

Another object is to provide means afiording stable operation of a gaseous tube at relatively low load currents, without afiecting its ultimate load current carrying capacity.

The drawings in addition to Fig. 1, which has already been described, include the following:

Fig. 2, illustrating a motor control system employing grid-controlled gaseous tubes to control the motor primary current;

Fig. 3 which is a modification oi the system of Fig. 2, employing ignitrons to carry the primary current;

Fig. 4 which is a modification oi the system of Fig. 2 and Fig. 3;

Figs. 5 and 6 which illustrate certain characteristics of the modifications of Figs. 3 and 4, respectively, while Fig. 7 which illustrates another modification of the systems shown in Figs. 2, 3 or 4.

Referring to Fig. 2, the same illustrates an induction motor Ill, having a three-phase primary winding llil and a three-phase secondary winding Ill. The primary winding is connectable to the bus bars L U, and L of a. threephase source of supply through an electromagnetic switch I I, having an energizingwindin I I, and normally open main contacts it, "H and li The contacts ll connect the bus bar L to one terminal of the winding i. The contacts ll connect the bus bar L3 to another terminal of winding l0 while the contacts H are connected between the bus bar L and the cathode l2 of a gaseous electron tube I2. A gaseous tube l3 has an anode I 3'' which is connected to the cathode l2 and a cathode l3 which is connected to the anode l2 of the tube H2. The tubes l2 and [3 are also provided with control electrodes I2 and B respectively. Connected across the lines L L is a center tapped impedance II. The center tap of the impedance I4 is connected to one terminal of said primary winding l5 of a transformer I 5. The other terminal of said primary winding. I5 is connected to one of the end terminals of the impedance it through a resistor I5, and is also connected to the other end terminal of the impedance H through thewinding ll of a sat-urable reactor H which is also provided with a saturating winding il The transformer I5 is also-provided with secondary windings li and. I5. The'winding I5 is connected between the cathode i2 and the control electrode l2 while the winding l5 is connected between the cathode i3 and the control electrode' 13.

The secondary winding l0 of the motor lilis connected to resistors l8, l9, and 20, one terminal of each resistor being connected to one phase each of the winding ill, while the other terminals of said resistors are connected together to form a star or neutral point. Each resistor is divided into three sections ll, [8", l8", I8, l9", and l9, and 20, 20 and 20, respectively. The three terminals of the motor winding Ill are connected to the three contacts 2| 01' a triple contact switch 2i which also has an energizing winding 2|. Similarly, the intermediate taps between the resistors I3, l3; l8, i8"; 20', 20 are connected to the three poles of a triple contact 22 of an electromagnetic switch 22 having an energizing winding 22" and the common terminals of the resistors [3 and l8, l9 and i3", and 20 and 20 are each connected to one Of the terminals of a triple contact switch 23 of an electromagnetic switch 23 which is also provided with an energizing winding 23. minal of the windings 21*, 22', and 23 is connected to the positive terminal of a direct current source 24 while the other terminals of said windings are connected to the anodes 25 26 and 21 of electron tubes 25, 26, and 21, respectively. These electron tubes are also provided with cathodes 25 26*, and 21, respectively, connected to the negative terminal of the voltage source 24 and with control electrodes 25, 26, and 21, respectively. A voltage dividing resistor 29, is connected between the positive and-negative terminals of a second direct current voltage source 28. The control electrode 2l is connected in series with a current limiting resistor 30 to an adjustable contact 29 of the voltage divider 29. The control electrode 26 is connected through a current limiting resistor 3| to a movable contact 29 of the voltage divider 28, while the control electrode 25 is connected through a current limiting resistor 32 to a third movable contact 28 of said voltage-divider 29.

Arranged so as to rotate with the armature of the motor I0 is a tachometer generator 33, the output voltage of which is proportional to the speed of the motor ID. The tachometer 33 may be of any suitable type yielding a unidirectional voltage. The diagram shows a tachometer generator which may be of the permanent magnet type or which may be provided with a separately excited field winding .(not shown).

The negative terminal of the generator 33 is connected through a current limitin resistor 34., to the control electrode 35 of an electron tube 35 which is also provided with a cathode 35 and an anode 35 The cathode 35- and anode 35 are connected to the negative and positive terminals respectively, of a direct current voltage source 36, the connection of the anode being through .a resistor 31. The anode 35 is also connected through a current limiting resistor to the control electrode 38 of an electron tube 38 which is also provided with an anode 38 connected through a resistor 39 to the positive terminal 01 the source 36 and with an anode 38* which is connected to the movable contact 40 of a voltage dividing resistor 40. The resistor 40 is connected across the terminals 01! the source 33. The anode 38 is directly connected to the control electrode ti of an electron tube ll, which is also provided with a cathode ll connected to the positive terminal of the voltage source 36 and with an anode li connected through a resistor 42 to one terminal of the winding I'I ofsaturable reactor II. The second terminal of the winding l'I is connected to the positive pole of a direct current voltage source 43'. The negative terminal of said voltage source 43 is connected to the One terpositive terminal of the voltage source 35. Connected across the terminals of the source 36 is a voltage dividing resistor 44 which is provided with adjustable contacts 44 and 46 To enable the press to be operated under diiierent onditions the system further includes a normally closed stop push button switch 43 and normally open inching, running, and threading .push button switches 48. 41 and 48, respectively.

There is further provided a running" electromagnetic relay 49, having an energizing winding 49, normally open contacts 45 48, and 4& and normally closed contacts 49 and a "threading relay as having an energizing winding 80 and normally open contacts to and 50.

A circuit extends irom line L to one terminal or the push button switch 45. The other termiml of switch 45 is connected to one terminal of each 01 the push button switches 46, 41 and 48 and also to one terminal of the contacts 50, 50, 49, and 49. The second terminal oi contacts 45, 50 and 49 are jointly connected to one terminal of the energizing winding II", the second terminal of which is connected to the line I The second terminal of contact 58 is con-' nected to the second terminal of switch 48 and to one terminal of the winding 50*. The second terminal of the winding 50'- is connected to the line L. The second terminal of the contact 41 is connected to one terminal the winding 49* and to the second terminal of contact 49". The second terminal of the winding 49 is connected to line L. The positive terminal of the tachometer 33 is connected to one terminal of each 0! the contacts 49 and 48. The second terminal of the contact 49 is connected to the adjustable contact 44 while the second terminal of the contact 49 is connected to the adjustable contact 44'.

The system thus far desribed and illustrated in Fig. 2 operates in the following manner: It the lines L L, L are energized and it is desired to start the press for running at full speed, the push button switch 41 is momentarily closed, thereby establishing a circuit from line L over contacts 45, 41, through winding 49 to line L. Thereupon the relay 49 responds and closure oi its contacts 49 establishes a maintaining circuit in parallel with switch 41 so that switch 41 may be released and relay 49 remains energized. The relay 49 also closes contacts 49 which completes the energizing circuit of winding II and the main switch II is actuated. Closure of contacts li connects the line L to the anode l3 and cathode l2 and thus one terminal of primary winding ill to line L Closure of contacts ii and ii connects the other two terminals of the motor winding ill to the lines I and I respectively. The motor thereupon begins to revolve and generates voltage in the tachometer 33.

As is well understood, the conduction of the gaseous tubes l2 and I3 is determined by the moment at which, during the respective positive halt-cycle, the tube ignites and this in .turn is determined by the phase relation of the corresponding grid potential relative to the line voltage impressed upon said tubes. With the equipment standing still, the current passing through the saturating winding l1 is a maximum, as will be hereinafter explained, with the result that the phase angle between the voltage impressed on tubes l2 and I3 and the voltage induced in the windings I! and IV due to the voltage obtaininginthewinding li isaminimumandthe tubes are therefore conducting during substantially their entire respective positive halt-cycle.

The voltage impressed on the control electrode 35 by the voltage divider 46 is of suiiiciently high positive value with respect to the cathode 35'- to render the tube 35 highly conducting while no opposing voltage is supplied through the generator 33 as long as the latter is standing still. The high current flowing through the tube 35 produces a relativesly high voltage drop through the resistor t'l So that the tube as by vlrture of its low grid potential has a relatively low eonductlvity which in turn produces a relatively low potential drop through the resistor 39 to ran-- der the control electrode M only slightly nega-' tive with respect to the cathode M and this in turn causes a relatively high current to flow from the positive terminal of the voltage source 33 through th saturating winding i1", resistor d2, through the tube ti to the negative terminal of the battery d3. Thus the reactor i1 is highly saturated and the current through the winding i1 is large, thereby affording a voltage in the winding it of transformer l5 and corresponding voltages in the windings i5 and [5 which are substantially in phase with the voltage impressed upon the tubes l2 and [3. As a result the motor receives a high current from the line and accelerates.

The voltages impressed upon the control electrodes of the tubes 25, Ze -and 21 are adjusted for progressively less negative biases with respect to the corresponding cathodes. As the motor accelerates, these negative voltages are counteracted by an opposing supplemental voltage generated by the tachometer 33 so that ultimately with increasing speed the negative potentials of the control electrodes aforementioned progressively change toward positive values and the tubes 21, 26, and 25 become successively sumciently conductive to raise the energizing current of the coils 23 22, and 2| to 'a value sufficient to close the contacts 23", 22 and 2i thereby successively cutting out steps of resistance in the secondary circuit of the motor to accelerate the same.

As the speed oi the motor increases, the

tachometer 33 also supplies a supplemental voltage to the grid 35 which is opposed to the voltage supplied by the voltage divider 44 with the result that with increasing speed of the motor he tube 35 becomes less conducting thus increasing the conduction of the tube 38 which in turn decreases the conduction of the tube 4i and thereby decreases the current in the winding M The decrease of the current in the winding l1 reduces the saturation of the reactor 11 thereby decreasing the current through the winding l1. This increases the retardation of the phase angle of the voltages in the windings I5, li and l5 with respect to the voltage of the lines L L, and L and thereby retards the moment of ignition during the respective positive half cycles of the tubes i2 and I3 and thus reduces the effective current supplied to one phase of the winding ll of the motor so as to maintain the speed of said motor at a constant value, determined by the adjustment of the sliding contacts 44 and If the press is to be stopped, it is merely necessary to operate the stop push button 45. This interrupts the current supplied to the energizing winding of the relay 49 and the relay op ns its maintaining circuit and also opens the energizing circuit of the electromagnetic switch winding I! thus disconnecting the motor from the line and 1 as will be apparent.

W. bringing the equipment back to its initial condition.

If it is desired to inch the press, that is, to rotate it step by step, by momentarily supplying current to the motor, the inch button @8 is depressed. This completes the energizing circuit of the electromagnetic main switch it from line L through switch contacts t6 and 46 through the energizing winding ii to line L and the motor primary winding It is again connected to the line as aforedescribed. The motor will turn over and if it attains a sumcient speed the accelerating switches M, 22, and 23 operate in the manner aforedescribed. However, for inching, it is usually desired that the speed which the motor attains be limited to a very low value. Therefore, biasing voltage which is impressed upon the control electrode 35 is adjusted to a lower value than for starting and runnin at full speed. This is accomplished by interrupting the circuit from the positive terminal of the tachometer 38 through the normally open contacts 69 to the sliding contact 454 and completing a circuit from the positive terminal of the tachometer 88 through the contacts 419 to the adjustable contact it", the relay to not being energized upon the depression of the inching button 38. Thus by adjusting the contact 66', the conduction of the tube may be adjusted for the maximum speed which the motor may attain upon depression of the inching button 38. This speed may be only a small percentage of the full load speed of the motor and may be insumcient to cause closure of any oi the accelerating switches 28 22 and it".

Ii it is desired to operate the press at a low threading speed, the slow push button switch it is closed. This energizes the windin ad by a circuit from line L through switches ig and 6d, the energizing winding bil to the line I The relay M responds to close a maintaining circuit through contact bil which parallels the switch 68 so that the relay W remains energized when the push button id is released. At the same time the contact 5b is closed thereby completing the energizing circuit for the ,main switch it from line L over contacts 65: and be, through the winding iii to line L. The motor speed is controlled by controlling the moment of ignition of the tubes i2 and is in response to the voltage impressed upon the tube 35 by the voltage divider .44 and the tachometer 33 in the manner aforedescribed. As the relay $9 is deenerglzed, the.

grid 35 is now controlled by the setting of the contact M.

It the motor is to be stopped when running at threading speed, it is merely necessary to operate the push button switch 48, which opens the maintainin circuit of the relay B8 and this in turn deenergizes the electromagnetic switch it The system illustrated in Fig. 2 embodies gridcontrolled gaseous discharge tubes i2 and It connected in series with the motor primary winding. Under certain conditions, especially for larger motors, it is desirable to use mercury pool tubes known as "ignitrons. In that case the system may be substantially the same as aforedescribed, except that the ignitrons are interposed in the motor circuit and are in turn controlled by thyra-- 3 tron tubes which are actuated in the manner aforedescribed.

Fig. 3 shows substantially only that part of the system which diflers'from that shown in Fig. 2. In the case of Fig. 3, the thyratron tubes control ii" and i3 0! the thyratrons l2 and I3, respec-' tively, are connected through current limiting resistors $8 and M, respectively, to the ignitron electrodes 82 and 68, respectively, of the cor-' responding ignitrons 82 and 63. The anode 83 of the ignitron lid is connected to the thyratron anodes i2 and is", respectively. The anode 62 of ignitron 62 is connected to the cathode 63 and to one terminal of winding i0. 62 is connected to the anode 63 and also through the contact W to the line L. It will be apparent that the current in the ignitrons is initiated at the moment when the corresponding thyratrons become conductin and the functioning of the system is in all other respects the same as has been explained in connection with Fig. 2.

It is well known that ignitrons will not operate successfully below a certain minimum current.

. Fig. 5 shows for a given load the voltage drop through an ignitron from zero conduction to conduction for practically the full time during whichits anode potential is positive with respect to the cathode. It also shows the minimum current (I min.) below which the ignitron will not function successfully. From this it will be seen that if the external impedance in series with the ignltron is very high so that the current through the tube would be less than the aforestated minimum, the ignitrondoes not function successfully in response to the effect of its ignitron electrode. Such conditions may obtain when the load on a motor which is controlled by the ignitron is very low, so that it would be diflicult if not impossible to obtain a very low creeping speed at low motor torques with the arrangement shown in Fig. 3.

Fig. 4 shows substantially only that part of the system which differs from that shown in Fig. 3. This arrangement provides for passing through the ignitron, in addition to the motor current, a supplemental current which together with the motor current maintains a sufliciently high current through the ignitron to cause it to function properly. This means consists oi. a saturable reactor the alternating current winding 64' of which is connected in parallel with the motor winding between the cathode B3 of the ignitron and the bus bar L of Fig. 3. The saturating winding 64 of said reactor is connected in series with a rectifier 66, across the main electrodes of the ignitron 88. To smooth out the half-wave rectified current passing through the tube 65, a smoothing condenser 68 is connected across the terminals of the winding 64*. It will be seen that the current which passes through the winding 84 is a direct function of the voltage drop across the ignitron 83. Hence when the voltage drop of the ignitron is high, the current in said winding 64 is high, whereas when the voltage across the ignitron'is low, the current in the winding 84 is low.

It is further known that the current in the winding 81'' varies with the current in the winding 64*. The current in the winding 64* is added to the current flowing through the tube 63 to the corresponding terminal of the motor winding. Thus the total current flowing through the tube The cathode is the resultant of the motor current and the current flowing through the reactor winding is.

Referring to Fig. 6, the tube current is indicated by a substantially straight line. The minimum current at which the tube will operate consistently is indicated by the letter A. Without the current through the winding 64 this would also be the minimum current to the motor, and the range through which the tube c'ould regulate the motor would be from the point C in the diagram to the full load or 100 per cent load current. As the tube current decreases, the voltage impressed upon the contacts N on the push button iii, a separate push button may be provided for the braking op eration. It will also be apparent that the switch 10 may be employed in connection with the modifications of Figs. 3 and 4.

It will be obvious that instead of a single mo= tor, a plurality of motors, whose primary terminals reactance winding 61* increases as indicated by winding 64 tends to decrease. As a result, a bal-' ance is obtained at a certain point between the saturating eifect of the winding 8i and the effect of the voltage drop through the tube 83 upon the winding 6i". At that point the reactor current again decreases with decreasing tube current as shown in Fig. 6. Nevertheless, for the minimum tube current value A. the current through the reactor has still a substantial value so that the lower current B is available for the motor winding. Hence the reactor extends the range of control of the motor to a much lower value as indicated by the diagram, as the minimum current supplied to the motor is the minimum tube current less the current passing through the reactor.

It is thus apparent that by the addition oi the saturable reactor, the reactance of which first decreases and thereafter again increases with decreasing motor current, the range of speed control by the tubes 82 and 83 can be correspondingly increased. In practice it has been found that the motor may be operated for threading at a speed as low as 1 per cent to 2 per cent of its synchronous speed.

Fig. 7 illustrates a modification of Fig. 2 for dynamic braking oi the motor to obtain a quick stop. In addition to the apparatus shown in Fig. 2, the system is provided with an electromagnetic switch 10, having an energizing winding 10", norlnally open contacts 10' and 10, and normally closed contacts 10". The contacts 10 are connected between the anode 12 and cathode l3, while the contacts 10 and 10 are connected in parallel with the contacts II and H respectively. The stop push button switch 45 of Fig. 2 is provided with additional normally open contacts 45, which are closed upon depression of the push button and upon opening of the normally closed contacts 45.

The modification shown in Fig. 7 operates in the following manner: If it is desired to stop the press after threading or running, the push button 45 is depressed, thereby disconnecting the motor from the line in the manner aforedescribed.

But as long as the push button switch 45 is held down, the contacts are closed, thereby establishing a circuit from line L over contacts 45 through winding III to line L". This energizes the switch It, thereby establishing a circuit from line L through contacts 10 tube ll, through the motor primary winding I through contact to line L, while the opening of the contacts 10 cuts the tube I! out of circuit. As long as the motor rotates, it therefore acts as an alternating current generator, its energy being dissipated as heat generated by the currents induced in its secondary winding, thereby bringing the motor quickly to a stop.

It will be apparent that instead of providing the are connected in parallel, may be controlled taintly in the manner aforedescribed. It is further apparent that a single tachometer with a single set or a plurality of the aforedescribed associated regulating devices may be employed to jointly con trol a plurality of motors, each provided with an individual impedance device.

In some cases it may be desirable to pass only part of the motor primarycurrent of one phase through the tubes [2 and ill of Fig. 2 or the tubes 32 and 63 of the system illustrated in Fig. 3 for control by such tubes. In such event a suitable impedance may be connected in parallel with the respective tubes. With this arrangement only the component of the total current which passes through the tubes is subject to control thereby and the minimum current supplied to the motor is the current conducted by the impedance when the tubes have been rendered non-conducting by the influence of the controlling eiiect imposed thereon.

I claim:

l. A method of controlling, through control of a single line connection thereof, a polyphase translating device having all terminals connected to the lines of a polyphase supply circuit which comprises making said single connection dependent upon an electronic discharge produced therein and regulating half cycles of such discharge in respect of ratio of conduction and nonconduction during half cycles individually, thereby to afford diflerent unbalanced conditions in the translating device in a stepless manner through a range which may extend from substantially balanced polyphase conditions to single phase condi= tions.

2. In a control system fora translating device, in combination, a source of polyphase current, a translating device having a polyphase winding including a plurality of terminals for connect' ing it to said source to receive current therefrom, space discharge means having a control element and being interposed between said source and one of said terminals, and means to impress upon said control element a potential varying in response to an operating characteristic of said device and regulating the ratio of conduction and nonconduction of said discharge means during individual half cycles to thereby afford, through potential regulation of a single terminal of the polyphase winding, current control through a range which may extend from substantially balanced polyphase condition of the translating device to single phase condition thereof.

3. In'a printing press control system or the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, space discharge means having a control element and being interposed between said source and one of said terminals, and means to impress upon said control element a potential varying in response to the speed of said motor and regulating the ratio of conduction and nonconduction of said discharge means during individual half cycles to thereby aiford, through potential regulation of a single 15 terminal or the motor primary winding, motor accents llli control through a range which may extend from substantially balanced polyphase condition of the motor to single phase condition thereof.

4. In a printing press control system or the like, in combination, a source of polyphase cur rent, a motor having a polyphase primary winding including a plurality of terminals for con necting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, means for impressing upon said control element an alternating potential whose frequency is that of said polyphase current, means affording a potential which varies with the speed of said motor, and means to superimpose a resultant of said varying potential upon said alternating potential to vary the lin pedance of said device in response to the speed of said motor to aflEord, through potential regulation of a single terminal of the motor primary winding, motor control through a range which may extend from substantially balanced polyphase condition of the motor to single phase condition thereof.

5. In a printing press control system and the like, in combination, a, source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, and a secondary winding, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, means for impressing upon said control element an alternating potential whose frequency is that of said polyphase current, means afiording a potential which varies with the speed of said motor, means to superimpose a resultant of said varying potential upon said alternating potential to vary the impedance of said device in response to the speed of said motor, a variable impedance connected to said secondary winding, and means to vary said impedance in response to said varying potential.

6. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, means for impressing upon said control element an alternating potential whose frequency is that of said polyphase current, means affording a potential which varies with the speed of said motor, and means to superimpose a resultant of said varying potential upon said alternating potential for varying the phase angle between the latter and the voltage impressed upon said device by said source to vary the impedance of said device in response to the speed of said motor. 7

'7. In a printing press control system and the like, in combination, a, source of polyphase current, a motor having a polyphase primary wind= ing including a. plurality of terminals for connecting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one of said terminals, a phase shifting network connected to said source and to said control element to impress a potential upon the latter, means affording a, voltage which varies with the speed of said motor, and means to impress upon said phase shifting network a resultant of said varying voltage to vary the impedance of said device in respouse to the speed of said motor.

8. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a single pair of space discharge devices connected inversely parallel to each other between one phase of said source and one of said terminals, each of said devices having a control electrode for varying its impedance, and means to impress upon said control electrodes a potential varying in response to the speed of said motor to thereby control the current passing through said devices.

9. In a printing press control system and the like, in combination, a source of polyphase cur rent, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source and a secondary winding, a pair of space discharge devices connected inversely parallel to each other and interposed between said source and one of saidterminals, each of said devices having a control electrode for varying its impedance, a variable impedance connected to said secondary winding, means to impress upon said control electrodes 9. potential varying in response to the speed of said motor to thereby control the current passing through said devices, and means to vary said impedance in response to said varying potential.

10. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, two space discharge devices, each having a control electrode for varying its impedance, means to connect said terminals to said source and to interpose one of said devices between said source and one of said terminals, commutating means connecting the other of said devices inversely parallel with said one device for operating said motor as a prime mover and operative to alternatively disconnect said other device from circuit and to connect two of said terminals to said source with said one device interposed between said one terminal and said source for supplying a rectified current to said winding for dynamic braking of said motor, and means to impress upon said control electrodes a potential varying in response to the speed of said motor to thereby control the current passing through said devices.

11. In a control system for a translating device, in combination, a source of alternatin current, a translating device having a winding including a plurality of terminals for connecting it to said source to receive current therefrom, space discharge means interposed between said source and one of said terminals, a variable impedance device connected between said one and another one of said terminals, and means for varying the impedance of said impedance device in accordance with the voltage drop through said discharge means.

12. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, space discharge means having a control element for varying the impedance thereof interposed between said source and one of said terminals, means to impress upon said control element a potential varying in response to the speed of said motor to thereby control the current passing through said space discharge means, a. variable impedance device connected between said one and another one of said terminals, and means for varying the impedance of said impedance device in accordance with the voltage drop through said space discharge means.

13. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a space discharge device having a control element for varying its impedance interposed between said source and one or said terminals, a phase shiftin network connected to said source and to said control electrode to impress a control potential upon the latter, means afiording a voltage which varies with the speed of said motor, means to impress upon said phase shifting network a resultant of said varying voltage to vary the impedance of said discharge device in response to the speed of said motor, a variable impedance device connected between said one and another one of said terminals, and means for varying the impedance of said impedance device in accordance with the voltage drop through said space discharge device.

14. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a pair of space discharge devices connected inversely parallel to each other and interposed between'one of said terminals and said source, each of said discharge devices having a control electrode, means affording a potential which varies with the speed of said motor, manual slow speed and high speed means for connecting said terminals to said source and interposing said space discharge deaffording different ratios between said varying I 15. In a printing press control system and the like, in combination, a source of polyphase current, a motor having a polyphase primary winding including a plurality of terminals for connecting it to said source, a first space discharge device, a second space discharge device, each of said devices having a control electrode for varying its impedance, means to impress upon saidcontrol electrodes a potential varying in response to the speed of said motor to thereby control the current passing through said devices, manual starting means operative to connect said winding through said terminals to said source and to interpose said first space discharge device between said source and one of said terminals for starting and running, and including means to connect said second space discharge device inversely parallel to said first space discharge device, and manual stopping means operative to disconnect said second space discharge device from circuit and render said starting means ineffective to thereby afiord dynamic braking.

WILLIAM H. ELLIOT.

REFERENCES CITED The followingireferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,376,453 Meyer May 3, 1921 1,914,350 Evans 1 June 13, 1933 2,386,581 Wicherham Oct. 9, 1945 

